Traditionally, local phone service has been provided to subscribers by a telephony service provider, such as a Regional Bell Operating Company (“RBOC”), via the Public Switched Telephone Network (“PSTN”). Because of recent technological developments and changes in regulatory laws, other types of entities, such as wireless service providers and cable service providers, now have an opportunity to compete with or supplant the traditional telephone company as the primary local phone service provider for many subscribers. As used herein, the terms “subscriber” or “customer” are defined as a user of cable services.
For a cable service provider to provide telephony service to a subscriber, the cable system generally requires a device known as a Network Interface Unit on or near the subscriber's premises to function as the interface between the subscriber's telephony equipment and the service provider's cable plant. As used herein when distinguishing the service provider's equipment from the subscriber's equipment, the term “cable plant” includes the cable service provider's transmission equipment and the Hybrid Fiber Coax (“HFC”) network used to propagate the cable service to the subscriber. As used herein, the term “Network Interface Unit” (or “NIU”) is defined to be the equipment which is used to interface between a subscriber's telephony equipment and the cable plant. The actual device that performs this interface function may be called by other names, or may perform additional functions. For example, the device may be called a Network Interface Device (“NID”), cable modem (“CM”), customer access unit, or wallbox. As another example, the device may perform other functions such as housing the ground block, providing a splitter, or providing an amplifier.
In order for a cable service provider to function as the primary local telephony service for a subscriber, however, the service provider must generally power the NIU through the cable so that guaranteed Quality of Service (“QoS”) is maintained even during a power outage at the subscriber's premises, in much the same way that the traditional telephone company powers a subscriber's phone. This capability is commonly known as “Lifeline Support” since it provides the subscriber with the ability to dial emergency services even during a power outage. The cable telephony service provider generally implements this feature by powering the NIU from storage batteries within the cable plant. Generally, it follows that the lower the average power dissipation of the NIU, the smaller the storage batteries for a given Lifeline Support duration, and therefore the lower the cost of offering that service, other factors being equal. Alternatively, the Lifeline Support duration may be made longer if the capacity of the storage batteries is kept constant. As used herein, the term “external power” is defined as power received from a source other than through the cable input to the NIU.
Accordingly, there is a need in the prior art for a NIU with a low average power dissipation to economically enable the provision of Lifeline Support service via cable telephony.